Table Lands of South India. 313 



The form of some of these ranges of hills has sometimes 

 suggested the idea, that they might have heen ei craters of 

 eruption," and the red ferruginous soils disintegrated lavas, 

 which filled the hollows upon the summit ; but I have never 

 been able to find any satisfactory trace of lavas about their 

 flanks. 



As the hornblendic rocks form a large proportion of the 

 schistose series of rocks in South India, it may be useful to 

 add a list of them with their characters, for the purpose of 

 identifying those which have been enumerated. 



The mineral, which forms the characteristic ingredient in 

 the following rocks, I have not been able to identify with any 

 European species. It answers in outward characters to 

 Jameson's definition ; but in chemical composition, it differs 

 widely from the proportions given by Thomson ; he makes it 

 a magnesian mineral, -but most of the specimens which I have 

 analyzed are very ferruginous, and contain little magnesia, 

 and approach more to the composition given by Thomson of 

 " Arfredsonite." 



Hornblende in the Salem district is rare as a pure mineral, 

 occurring almost always in conjunction with others, and the 

 crystals being generally small and often amorphous, the crys- 

 talline form gives but little help. 



I have specimens of compound rocks formed of this 

 mineral, which shew a perfect graduation from the black 

 varieties of perfect black granite up to a rock which has a 

 grey-coloured fracture, and which to the bruise of the ham- 

 mer shews a considerable quantity of magnesia in its com- 

 position. I have found it to approach closely to Dr. Thom- 

 son's composition of hornblende. 



I may here remark, that the appearance of the bruise by a 



heavy hammer is a very correct indication of the quantity of 



magnesia contained in a compound rock; the whiteness of 



the appearance of the bruise shewing the most magnesia. 



Crystalline hornblende. — Formed entirely of crystals, or 



